This disclosure relates to measuring positions of objects. Noncontact measuring of positions of objects is achieved through measurements of parameters characterizing the distribution of an AC magnetic field in an air gap between stationary and moveable portions of the sensor magnetic circuit.
Inductive, reluctance and eddy-current position sensors allow noncontact measurements of object positions using electromagnetic fields. These sensors consist of stationary portions commonly referred to as sensor heads and movable portions, commonly referred to as sensor targets. For example, sensors 1500a-b and 1600a-b shown in FIGS. 15a-b and FIGS. 16a-b, respectively, consist of sensor heads 1502 and 1602 and sensor targets 1504 and 1604. The sensors 1500 and 1600 serve to measure displacements of the sensor targets 1504 and 1604 along the Z-axes 1512 and 1612. The difference between the devices shown in FIGS. 15a-b and 16a-b is that in FIGS. 15a-b the distance from the sensor target 1504 to the sensor heads 1502 changes when the sensor target 1504 moves along the Z-axis 1512, whereas in FIGS. 16a-b the distance from the sensor target 1604 to the sensor heads 1602 remains the same. In order to function, however, the sensors shown in FIGS. 16a-b require the sensor target 1604 be composed of at least two parts 1616 and 1618 with different electromagnetic properties stacked in the Z-direction. The sensor heads 1502 and 1602 include at least one coil 1520 and 1620 wound around cores 1506 and 1606. The cores 1506 and 1606 can be made out of a soft-magnetic material, or can be absent. If there is only one coil 1502 or 1602 wound around each sensor core 1506 or 1606, the position of the sensor target 1504 or 1604 is determined based on the change of the coil impedance with the target position in the direction of the Z-axis 1512 or 1612. In some sensors, there might be two coils 1502 or 1602 in each sensor head wound around a common soft-magnetic core. One of the coils—an exciter coil—is used to generate a magnetic flux in the magnetic circuit, whereas the other—a receiver coil—is used to measure a portion of the magnetic flux generated by the exciter coil which penetrates the receiver coil. In this case, the measurement of the position of the sensor target along the Z-axis 1512 or 1612 can be based on the measurement of the mutual inductance between the coils or the portion of the flux generated by one coil that penetrates the other coil. Using two sensor heads 1502a and 1502b located on the opposite faces of the sensor target 1504 with reference to the Z-axis 1512 in FIG. 15b, rather the single sensor head 1502 in FIG. 15a, allows achieving a more linear relationship between the sensor output and the sensor target displacement. Using two sensor heads 1605a and 1605b located on the opposite faces of the sensor target 1604 with reference to the X-axis 1648 in FIG. 16b rather the single sensor head in FIG. 16a, allows minimizing effects of the sensor target displacements in the X-direction on the sensor output.